Microsoft has quietly started swapping out the AI brains behind Excel and Outlook. As of July 7, 2026, the company began routing a meaningful share of Copilot prompts in those two apps to its own internally built MAI models, stepping back from its reliance on OpenAI and Anthropic for the kind of everyday, high-volume tasks that add up fast on an inference bill.
What is actually changing
The MAI models, short for Microsoft AI, are now handling tens of thousands of prompts weekly inside Excel and Outlook. These are the bread-and-butter requests: summarizing an email thread, drafting a reply, formatting a spreadsheet, that sort of thing.
Microsoft has been clear that this is not a full divorce from its external partners. OpenAI’s frontier models will continue to power more complex, demanding tasks where raw capability still matters. Anthropic’s models also remain embedded in specific Office applications for select use cases.
The MAI models themselves were introduced at Microsoft’s Build conference in June 2026, where the company unveiled MAI-Thinking-1 and MAI-Code-1-Flash as part of a broader push to establish its own presence in the AI model landscape. The Build showcase framed these models as competitive in quality while being cheaper to operate.
